Sigma AF 18-50mm f/2.8 EX DC macro - Review / Lab Test Report
Lens Reviews - Nikon / Nikkor (APS-C)
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Review by Klaus Schroiff, published February 2007

Lens kindly provided for testing purposes by Michael Kaufmann!


The Sigma AF 18-50mm f/2.8 EX DC macro is one of the more interesting third-party standard zooms thanks to a comparatively large max. aperture. It is already the 2nd incarnation of its kind by Sigma. Besides a change in the optical design the new variant offers a shorter min. focus distance of just 20cm resulting in a max. magnification of 1:3 @ 50mm - therefore the new "macro" addition in the lens' name. Nonetheless it is not a "true" macro lens because the focus group does not feature a floating elements design (typically found in dedicated macro fix-focal lenses) for improved close up performance. At a price around 400US$/EUR the penalty on your bank account would remain quite manageable. The Sigma is a DC ("Digital Camera") lens specifically designed for APS-C DSLRs where its field-of-view is equivalent to ~27-75mm on classic full format cameras. The lens is available in all major AF DSLR mounts (tested on the Nikon D200 here).

For whatever reason Sigma did not release any HSM standard zoom to date and the 18-50mm f/2.8 EX DC macro follows this tradition - on Nikon it relies on a slotted AF drive screw operated by the camera. Speed-wise there's no need for an ultrasonic drive whatsoever - due to a very short focus path (~45 degrees) the AF performance is very fast. On the downside this design results in rather delicate manual focusing and AF accuracy could be better. Thanks to internal focusing (IF) the front element does not rotate during focusing. Unfortunately the focus ring does rotate in AF mode which isn't really something to be proud of these days.

Similar to other EX ("Excellence") lenses the build quality is very decent but a little worse compared to the more pricey EX lenses or pro grade lenses from the genuine manufacturers. The lens features the typical EX crinkle finish and broad rubberized control rings. Both the focus and zoom rings operate very smooth. Sigma also implemented a zoom lock in order to prevent zoom creeping during transportation.

Equiv. focal length27-75 mm (full format equivalent)
Equiv. aperturef/4.2 (full format equivalent, in terms of depth-of-field)
Optical construction15 elements in 13 groups inc. 2x aspherical, 1x SLD and 1x ELD elements
Number of aperture blades7
min. focus distance0.20 m (max. magnification ratio 1:3)
Dimensions79 x 86 mm
Weight450 g
Filter size72 mm (non-rotating)
Hoodpetal-shaped (snap-on type)
Other features-

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